The present invention relates generally to stereotactic radiotherapy apparatus and particularly to a revolving or moving stack of collimators for shaping a radiation beam for performing stereotactic radiotherapy.
In stereotactic radiotherapy, a radiation source produces a radiation beam for irradiating a target tissue. A collimator is generally placed at the outlet end of the radiation source in order to shape the radiation beam to a desired diameter. In certain radiotherapy treatment plans, it may be required to irradiate the target tissue with several different diameter radiation beams. This generally requires dismantling a first collimator and replacing it with a second collimator of a different diameter and so forth. Such a procedure is inconvenient and time-consuming.
There are systems with multiple collimators in the prior art. Japanese Patent Document 6-233831 assigned to Hitachi describes a collimator revolver on which several numbers of collimators can be mounted. The collimator revolver is located near a collimator head of a radiotherapy device. The collimator head has a sliding mechanism which can grasp one of the collimators from the collimator revolver and slide the selected collimator into position on the collimator head so that the selected collimator is aligned with a radiation source.
U.S. Pat. No. 5,757,886 to Shipeng Song describes a system in which a plurality of radioactive sources are mounted in a base wherein all of the sources are radially aligned with a common focus on the central axis of the base. Coaxially aligned with the central axis is a collimator base containing a plurality of collimators of different aperture diameter. The collimator base can be rotated about the central axis so as to selectively align a particular collimator with one of the radiation sources.
The present invention seeks to provide a novel revolving collimator system which can shape a radiation beam emanating from a radiation source with a plurality of mutually alignable collimators and pre-collimators. The collimators and pre-collimators are mounted on a revolving plates preferably stacked along a common axis like a xe2x80x9clazy susanxe2x80x9d. A control system with servomotors selectively rotates any of the collimator plates, thereby aligning a plurality of collimators to form a path for collimating a radiation beam. The present invention thus collimates and pre-collimates radiation beams over a wide range of diameter apertures suitable for virtually any kind of radiotherapy treatment plan.
There is thus provided in accordance with a preferred embodiment of the present invention a collimator system including a plurality of revolvable plates stacked one above another, the plates being constructed of a material substantially impervious to passage therethrough of radiation in a predetermined range of wavelengths, and at least one collimator aperture formed in each of the plates.
In accordance with a preferred embodiment of the present invention the plates are arranged relative to each other such that the collimator apertures formed in neighboring plates are alignable with each other to form a collimation path adapted for a radiation beam to pass therethrough.
Further in accordance with a preferred embodiment of the present invention the plates are arranged to revolve about a common axis.
Still further in accordance with a preferred embodiment of the present invention one of the collimator apertures on one of the plates has a different sized opening than a collimator aperture on another of the plates.
Additionally in accordance with a preferred embodiment of the present invention at least one of the plates is formed with a plurality of differently sized collimator apertures.
In accordance with a preferred embodiment of the present invention at least one of the plates is formed with a plurality of generally equally sized collimator apertures.
Further in accordance with a preferred embodiment of the present invention at least one of the plates has a thickness different from another of the plates.
Still further in accordance with a preferred embodiment of the present invention a gap between neighboring plates of the plurality of revolvable plates is sufficiently small such that a radiation beam of a predetermined wavelength is substantially prevented from passing through the gap.
Additionally in accordance with a preferred embodiment of the present invention a controller is connected to the plates which selectively revolves the plates.
In accordance with a preferred embodiment of the present invention the controller includes a servomotor linked to the plates which selectively revolves the plates.
Further in accordance with a preferred embodiment of the present invention a subset of the plates are mechanically linked together and are mounted on bearings about a common axle, such that the subset of plates revolves together independently of the other plates.
Still further in accordance with a preferred embodiment of the present invention a stop mechanism selectively arrests rotational movement of the plates.